Methods and systems for adaptive base flow

ABSTRACT

This disclosure describes systems and methods for providing novel adaptive base flow scheduling during ventilation of a patient to optimize the accuracy of estimated exhaled tidal volume. Further, this disclosure describes systems and methods for providing novel adaptive inspiratory trigger threshold scheduling during the novel adaptive base flow scheduling.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patent application Ser. No. 13/313,128(now U.S. Pat. No. 9,364,624), entitled “METHODS AND SYSTEMS FOR ADAPTIVE BASE FLOW,” filed on Dec. 7, 2011, the entire disclosure of which is hereby incorporated herein by reference.

INTRODUCTION

Medical ventilator systems have long been used to provide ventilatory and supplemental oxygen support to patients. These ventilators typically comprise a source of pressurized oxygen which is fluidly connected to the patient through a conduit or tubing. Further, ventilators often measure and calculate various ventilator and/or patient parameters during the ventilation of a patient. For example, spirometry data provides valuable information for patient evaluation and clinical decision making. Accordingly, the accuracy of the spirometry data is an important performance characteristic of ventilators.

ADAPTIVE BASE FLOW

This disclosure describes systems and methods for providing novel adaptive base flow scheduling during ventilation of a patient to optimize the accuracy of estimated exhaled tidal volume. Further, this disclosure describes systems and methods for providing novel adaptive inspiratory trigger threshold scheduling during the novel adaptive base flow scheduling.

In part, this disclosure describes a method for ventilating a patient with a ventilator. The method includes:

a) determining an initial base flow;

b) determining an initial inspiration trigger threshold;

c) delivering the initial base flow during at least a first portion of exhalation while setting the inspiration trigger threshold to the initial inspiration trigger threshold;

d) determining a desired base flow;

e) determining a desired inspiration trigger threshold;

e) increasing base flow from the initial base flow toward the desired base flow during at least a second portion of exhalation; and

f) making the inspiration trigger threshold more sensitive by decreasing the inspiration trigger threshold from the initial inspiration trigger threshold toward the desired inspiration trigger threshold based on a function of the step of increasing the base flow while performing the step of increasing the base flow

Yet another aspect of this disclosure describes a method for ventilating a patient with a ventilator. The method includes:

a) determining an initial base flow;

b) determining an initial inspiration trigger threshold;

c) delivering the initial base flow during at least a first portion of exhalation while setting the inspiration trigger threshold to the initial inspiration trigger threshold;

d) increasing base flow from the initial base flow toward a first flow value during at least a second portion of exhalation; and

e) making the inspiration trigger threshold more sensitive by decreasing the inspiration trigger threshold from the initial inspiration trigger threshold toward a first trigger threshold value while performing the step of increasing the base flow

The disclosure further describes a ventilator system that includes: a pressure generating system adapted to generate a flow of breathing gas; a ventilation tubing system including a patient interface for connecting the pressure generating system to a patient; at least one sensor operatively coupled to at least one of the pressure generating system, the patient, and the ventilation tubing system; a base flow trajectory module for delivering a base flow during exhalation; an inspiratory trigger trajectory module sets an inspiration trigger threshold during the exhalation; and a processor in communication with the pressure generating system, the at least one sensor, inspiratory trigger trajectory module, and the base flow trajectory module. The base flow trajectory module determines an initial base flow to deliver during at least a first portion exhalation. The base flow trajectory module increases the base flow delivered to the patient circuit tubing from the initial base flow toward a desired base flow during at least a second portion of the exhalation. The inspiratory trigger trajectory module sets an initial inspiration trigger threshold while delivering the initial base flow. The inspiratory trigger trajectory module decreases the inspiration trigger threshold from the initial inspiration trigger threshold towards a desired inspiration trigger threshold while the base flow trajectory module increases the base flow delivered to the patient.

The disclosure additionally describes a computer-readable medium having computer-executable instructions for performing a method for ventilating a patient with a ventilator. The method includes:

a) repeatedly determining an initial base flow;

b) repeatedly determining an initial inspiration trigger threshold;

c) repeatedly delivering the initial base flow during at least a first portion of exhalation while setting the inspiration trigger threshold to the initial inspiration trigger threshold;

d) repeatedly increasing base flow from the initial base flow toward a first flow value during at least a second portion of exhalation; and

e) repeatedly decreasing an inspiration trigger threshold from the initial inspiration trigger threshold toward a first trigger threshold value while performing the step of increasing the base flow.

The disclosure also describes a ventilator system including means for determining an initial base flow, means for determining an initial inspiration trigger threshold, means for delivering the initial base flow during at least a first portion of exhalation while setting the inspiration trigger threshold to the initial inspiration trigger threshold, means for increasing base flow from the initial base flow toward a first flow value during at least a second portion of exhalation, and means for decreasing an inspiration trigger threshold from the initial inspiration trigger threshold toward a first trigger threshold value while performing the step of increasing the base flow.

These and various other features as well as advantages which characterize the systems and methods described herein will be apparent from a reading of the following detailed description and a review of the associated drawings. Additional features are set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the technology. The benefits and features of the technology will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawing figures, which form a part of this application, are illustrative of embodiments of systems and methods described below and are not meant to limit the scope of the invention in any manner, which scope shall be based on the claims.

FIG. 1 illustrates an embodiment of a ventilator.

FIG. 2 illustrates an embodiment of a method for ventilating a patient on a ventilator.

FIG. 3A illustrates an embodiment of a first portion of a method for ventilating a patient on a ventilator.

FIG. 3B illustrates an embodiment of a second portion of the method shown in FIG. 3A for ventilating a patient on a ventilator.

FIG. 4 illustrates an embodiment of a graph of delivered base flow and a set inspiration trigger threshold over time during an exhalation.

DETAILED DESCRIPTION

Although the techniques introduced above and discussed in detail below may be implemented for a variety of medical devices, the present disclosure will discuss the implementation of these techniques in the context of a medical ventilator for use in providing ventilation support to a human patient. A person of skill in the art will understand that the technology described in the context of a medical ventilator for human patients could be adapted for use with other systems such as ventilators for non-human patients and general gas transport systems.

Medical ventilators are used to provide a breathing gas to a patient who may otherwise be unable to breathe sufficiently. In modern medical facilities, pressurized air and oxygen sources are often available from wall outlets. Accordingly, ventilators may provide pressure regulating valves (or regulators) connected to centralized sources of pressurized air and pressurized oxygen. The regulating valves function to regulate flow so that respiratory gas having a desired concentration of oxygen is supplied to the patient at desired pressures and rates. Ventilators capable of operating independently of external sources of pressurized air are also available.

Spirometry data provides valuable information for patient evaluation and clinical decision making. Accordingly, the accuracy of the spirometry data is an important performance characteristic of ventilators. Spirometry volumes may be calculated by integrating the net flow, which is a linear combination of flow rates measured by a number of flow sensors at both the inspiration (delivery) side and at the exhalation (exhaust) side. These flow sensors possess different uncertainties and the overall accuracy performance is a function of a combination of the properties of individual devices. Exhaled tidal volume is measured during the expiratory phase of a ventilator breath while a base flow is delivered through the patient circuit. To determine the volume of gas exhaled by the patient, the net flow (total delivered flow minus total flow through exhalation module) is used for integration. That is, the delivered base flow is subtracted from the sum of the base flow and patient flow exiting through the exhalation port. Delivered flow during exhalation is base flow and consists of a desired combination of appropriate gases. The flow exiting the exhalation module during the active phase of patient exhalation is the sum of base flow delivered by the ventilator and exhaled flow from the patient lung. The spirometry parameter of exhaled tidal volume is measured during patient's active exhalation. Therefore, the smaller the ventilator-delivered base flow is during active exhalation, the smaller the uncertainty contributed by measuring the same quantity by different sensors (once on the delivery side and a second time as a portion of exhaust gas on the exhalation side). This is particularly advantageous under neonatal conditions when tidal volumes and exhaled flow rates are relatively smaller and may be some orders of magnitude smaller than the base flow.

Accordingly, the systems and methods described herein provide ventilation with an adaptive base flow initiation scheduling strategy to optimize the accuracy of estimated exhaled tidal volume. However, changing base flow during exhalation may affect inspiration triggering and lead to a false triggering of inspiration prior to a patient desired inspiration. Accordingly, the systems and methods described herein also provide ventilation with an adaptive trigger threshold initiation scheduling strategy to prevent undesired triggering of inspiration. For example, during a first exhalation portion when it is unlikely that a patient would attempt to initiate an inspiration, the inspiration trigger threshold is set very high. Further, the longer the exhalation period, the more likely it is that a patient would attempt to trigger a desired inspiration. Therefore, as the exhalation progresses or during a second portion exhalation, the inspiration trigger threshold is decreased making it easier for a patient to initiate a desired inspiration.

FIG. 1 is a diagram illustrating an embodiment of an exemplary ventilator 100 connected to a human patient 150. Ventilator 100 includes a pneumatic system 102 (also referred to as a pressure generating system 102) for circulating breathing gases to and from patient 150 via the ventilation tubing system 130, which couples the patient 150 to the pneumatic system 102 via an invasive (e.g., endotracheal tube, as shown) or a non-invasive (e.g., nasal mask) patient interface 180.

Ventilation tubing system 130 (or patient circuit 130) may be a two-limb (shown) or a one-limb circuit for carrying gases to and from the patient 150. In a two-limb embodiment, a fitting, typically referred to as a “wye-fitting” 170, may be provided to couple a patient interface 180 (as shown, an endotracheal tube) to an inspiratory limb 132 and an expiratory limb 134 of the ventilation tubing system 130.

Pneumatic system 102 may be configured in a variety of ways. In the present example, pneumatic system 102 includes an expiratory module 108 coupled with the expiratory limb 134 and an inspiratory module 104 coupled with the inspiratory limb 132. Compressor 106 or other source(s) of pressurized gases (e.g., air, oxygen, and/or helium) is coupled with inspiratory module 104 and the expiratory module 108 to provide a gas source for ventilatory support via inspiratory limb 132.

The inspiratory module 104 is configured to deliver gases to the patient 150 according to prescribed ventilatory settings. In some embodiments, inspiratory module 104 is configured to provide ventilation according to various breath types.

The expiratory module 108 is configured to release gases from the patient's lungs according to prescribed ventilatory settings. The expiratory module 108 is associated with and/or controls an expiratory valve for releasing gases from the patient 150. Further, the expiratory module 108 may instruct the pressure generating system 102 and/or the inspiratory module 104 to deliver a base flow during exhalation.

The ventilator 100 may also include one or more sensors 107 communicatively coupled to ventilator 100. The sensors 107 may be located in the pneumatic system 102, ventilation tubing system 130, and/or on the patient 150. The embodiment of FIG. 1 illustrates a sensor 107 in pneumatic system 102.

Sensors 107 may communicate with various components of ventilator 100, e.g., pneumatic system 102, other sensors 107, expiratory module 108, inspiratory module 104, processor 116, controller 110, trigger module 115, inspiratory trigger trajectory module 117 (illustrated as “ITT Module”), base flow trajectory module 118 (illustrated as “Base Flow Traj. Module”), Leak Estimation Module 119 (illustrated as “Leak Est. Module), and any other suitable components and/or modules. In one embodiment, sensors 107 generate output and send this output to pneumatic system 102, other sensors 107, expiratory module 108, inspiratory module 104, processor 116, controller 110, trigger module 115, inspiratory trigger trajectory module 117, base flow trajectory module 118, leak estimation module 119, and any other suitable components and/or modules.

Sensors 107 may employ any suitable sensory or derivative technique for monitoring one or more patient parameters or ventilator parameters associated with the ventilation of a patient 150. Sensors 107 may detect changes in patient parameters indicative of patient inspiratory or expiratory triggering, for example. Sensors 107 may be placed in any suitable location, e.g., within the ventilatory circuitry or other devices communicatively coupled to the ventilator 100. Further, sensors 107 may be placed in any suitable internal location, such as, within the ventilatory circuitry or within components or modules of ventilator 100. For example, sensors 107 may be coupled to the inspiratory and/or expiratory modules for detecting changes in, for example, circuit pressure and/or flow. In other examples, sensors 107 may be affixed to the ventilatory tubing or may be embedded in the tubing itself. According to some embodiments, sensors 107 may be provided at or near the lungs (or diaphragm) for detecting a pressure in the lungs. Additionally or alternatively, sensors 107 may be affixed or embedded in or near wye-fitting 170 and/or patient interface 180. Indeed, any sensory device useful for monitoring changes in measurable parameters during ventilatory treatment may be employed in accordance with embodiments described herein.

As should be appreciated, with reference to the Equation of Motion, ventilatory parameters are highly interrelated and, according to embodiments, may be either directly or indirectly monitored. That is, parameters may be directly monitored by one or more sensors 107, as described above, or may be indirectly monitored or estimated by derivation according to the Equation of Motion or other known relationships.

The pneumatic system 102 may include a variety of other components, including mixing modules, valves, tubing, accumulators, filters, etc. Controller 110 is operatively coupled with pneumatic system 102, signal measurement and acquisition systems, and an operator interface 120 that may enable an operator to interact with the ventilator 100 (e.g., change ventilator settings, select operational modes, view monitored parameters, etc.).

In one embodiment, the operator interface 120 of the ventilator 100 includes a display 122 communicatively coupled to ventilator 100. Display 122 provides various input screens, for receiving clinician input, and various display screens, for presenting useful information to the clinician. In one embodiment, the display 122 is configured to include a graphical user interface (GUI). The GUI may be an interactive display, e.g., a touch-sensitive screen or otherwise, and may provide various windows and elements for receiving input and interface command operations. Alternatively, other suitable means of communication with the ventilator 100 may be provided, for instance by a wheel, keyboard, mouse, or other suitable interactive device. Thus, operator interface 120 may accept commands and input through display 122.

Display 122 may also provide useful information in the form of various ventilatory data regarding the physical condition of a patient 150. The useful information may be derived by the ventilator 100, based on data collected by a processor 116, and the useful information may be displayed to the clinician in the form of graphs, wave representations, pie graphs, text, or other suitable forms of graphic display. For example, patient data may be displayed on the GUI and/or display 122. Additionally or alternatively, patient data may be communicated to a remote monitoring system coupled via any suitable means to the ventilator 100. In some embodiments, the display 122 may illustrate a minimum exhalation flow, a minimum exhalation time, a maximum exhalation time, a desired base flow, a desired inspiration trigger, an inspiration trigger, a base flow, an exhalation flow, an estimated leak flow, an exhalation pressure, and/or any other information known, received, or stored by the ventilator 100.

In some embodiments, controller 110 includes memory 112, one or more processors 116, storage 114, and/or other components of the type commonly found in command and control computing devices. Controller 110 may further include an inspiratory trigger trajectory module 117, a base flow trajectory module 118, a trigger module 115, and/or a leak estimation module 119 as illustrated in FIG. 1. In alternative embodiments, the inspiratory trigger trajectory module 117, the base flow trajectory module 118, trigger module 115, and/or the leak estimation module 119 are located in other components of the ventilator 100, such as in the pressure generating system 102 (also known as the pneumatic system 102).

The memory 112 includes non-transitory, computer-readable storage media that stores software that is executed by the processor 116 and which controls the operation of the ventilator 100. In an embodiment, the memory 112 includes one or more solid-state storage devices such as flash memory chips. In an alternative embodiment, the memory 112 may be mass storage connected to the processor 116 through a mass storage controller (not shown) and a communications bus not shown). Although the description of computer-readable media contained herein refers to a solid-state storage, it should be appreciated by those skilled in the art that computer-readable storage media can be any available media that can be accessed by the processor 116. That is, computer-readable storage media includes non-transitory, volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. For example, computer-readable storage media includes RAM, ROM, EPROM, EEPROM, flash memory or other solid state memory technology, CD-ROM, DVD, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by the computer.

The base flow trajectory module 118 determines the amount of base flow to deliver to the patient circuit tubing during exhalation. The base flow trajectory module delivers a constant base flow during a first portion of exhalation and then varies the base flow delivered during at least a part of a second portion of exhalation. Accordingly, the base flow trajectory module 118 determines an initial base flow to deliver during a first portion of exhalation. In some embodiments, the initial base flow is input or selected by the operator. In other embodiments, the initial base flow is determined by the ventilator 100 based on the configuration of the ventilator 100 and/or based on ventilator and/or patient parameters and settings. The first portion of exhalation includes at least the beginning or start of the exhalation period. In some embodiments, the first portion of exhalation is a minimum exhalation time. The “minimum exhalation time” as referred to herein is a predetermined amount of time in which it is unlikely that a patient would desire to begin inspiration or would attempt to trigger an inspiration. The base flow trajectory module 118 instructs the inspiratory module 104 to deliver the initial base flow at the beginning of inhalation. In further embodiments, the base flow trajectory module 118 delivers the initial base flow at the beginning of the first portion of exhalation or for the entire duration of the first portion of exhalation.

The base flow trajectory module 118 may also determine a desired base flow. In some embodiments, the desired base flow is input or selected by the operator. In other embodiments, the desired base flow is determined by the ventilator 100 based on the configuration of the ventilator 100 and/or based on ventilator and/or patient parameters.

The base flow trajectory module 118 instructs the inspiratory module 104 to increase the delivered base flow from the initial base flow towards a first flow value, such as the desired base flow, during at least a second portion of exhalation. The second portion of exhalation does not overlap with the first portion of exhalation. Accordingly, the second portion of exhalation does not include the beginning of exhalation, but may begin immediately thereafter.

The second portion of exhalation starts or begins based on the occurrence of a condition. The base flow trajectory module 118 may determine the occurrence of the condition based on output received from sensors 107. Accordingly, in some embodiments, the base flow trajectory module 118 instructs the inspiratory module 104 to increase the base flow from the initial base flow towards the desired base flow after determining the occurrence of a condition. In some embodiments, the condition includes determining that a minimum exhalation time has expired, determining that a monitored exhalation flow is below the minimum exhalation flow; determining that the monitored exhalation flow is below the minimum exhalation flow prior to expiration of a maximum exhalation time, and/or determining that the maximum exhalation time has expired. In other embodiments, the condition includes determining that a minimum exhalation time has expired and determining that either a monitored exhalation flow is below the minimum exhalation flow prior to expiration of a maximum exhalation time or the maximum exhalation time has expired. The maximum exhalation time is a predetermined amount of time after which it becomes highly likely that a patient would attempt to trigger inspiration. The minimum exhalation flow is a predetermined flow rate that when exhaled by the patient indicates that a patient is approaching the end of active exhalation. In some embodiments, the base flow trajectory module 118 instructs the inspiratory module 104 to increase the delivered base flow from the initial base flow towards a first flow value at the start of a second portion of exhalation or for the entire duration of the second portion exhalation.

In embodiments, the base flow trajectory module 118 instructs the inspiratory module 104 to increase the base flow at an exponential trajectory. In some embodiments, the exponential trajectory is based on a time constant that is indicative of the expected response time from the initial point to the final desired flow target. The time constant may be determined by the ventilator 100 based on the ventilator configuration or based on ventilator and/or patient parameters. In other embodiments, the time constant is input or selected by the operator.

In further embodiments, the base flow trajectory module 118 instructs the inspiratory module 104 to increase the base flow until the delivered base flow is essentially or substantially the first flow value, such as a desired base flow. Once the delivered base flow substantially reaches the first flow value, the base flow trajectory module 118 instructs the inspiratory module 104 to deliver the first flow value. The first flow value is substantially reached or essentially reached when the ventilator 100 can no longer increase the amount of base flow provided without reaching or exceeding the first flow value based on the sensitivity and precision of the ventilator components.

In some embodiments, the initial base flow is zero. In other embodiments, the initial base flow is zero plus an estimated leak. Accordingly, in some embodiments, the ventilator 100 utilizes a leak estimation module 119. The leak estimation module 119 estimates the amount of flow leaking from the ventilation tubing system 130 utilizing any conventionally known methods. The estimated leak determined by the leak estimation module 119 is then added to the initial base flow to compensate for the amount of flow lost from the ventilation tubing system 130 during ventilation. Further, the estimated leak may be added to the first flow value, such as the desired flow, to compensate for the amount of flow lost from the ventilation tubing system 130 during ventilation.

Ventilators 100, depending on their mode of operation, may trigger automatically and/or in response to a detected change in a ventilator and/or patient parameter. The trigger module 115 receives and/or determines one or more inspiration trigger thresholds. In some embodiments, the trigger module 115 receives an inspiration trigger threshold from the ITT Module 117. In other embodiments, the trigger module 115 determines an inspiration trigger threshold based on ventilator and/or patient parameters and/or the ventilator configuration. For example, the ventilator may be preconfigured to deliver an inspiration after a predetermined amount of exhalation time to prevent a patient from becoming under-ventilated. In other embodiments, the trigger module 115 receives an inspiration trigger threshold from operator input or selection.

During exhalation, the trigger module 115 monitors ventilator and/or patient parameters and compares these parameters to one or more inspiration trigger thresholds to determine if the parameters meet and/or exceed the inspiration trigger thresholds. Sensors 107 suitable for this detection may include any suitable sensing device as known by a person of skill in the art for a ventilator 100. If the trigger module 115 determines that ventilator and/or patient parameters meet and/or exceed an inspiration trigger threshold during exhalation, the trigger module 115 instructs the inspiratory module 104 to deliver an inspiration, which effectively ends the exhalation phase controlled by the expiratory module 108. If the trigger module 115 determines that ventilator and/or patient parameters do not meet and/or exceed an inspiration trigger threshold during exhalation, the trigger module 115 continues to monitor the ventilator and/or patient parameters and compare them to a trigger threshold until the ventilator and/or patient parameters meet and/or exceed a trigger threshold.

In some embodiments, the trigger module 115 of the ventilator 100 detects changes in a ventilator and/or patient parameter via the monitoring of a respiratory gas pressure, the monitoring of lung flow, direct or indirect measurement of nerve impulses, or any other suitable method for detecting changes in a ventilator parameter. In embodiments where changes in a ventilator parameter are detected by monitoring flow and/or pressure, the sensitivity of the ventilator 100 to changes in pressure and/or flow, may be adjusted. For example, the lower a pressure or flow change trigger threshold setting, the more sensitive the ventilator 100 may be to a patient initiated trigger. However, each ventilator 100 will have a minimum measurable inspiration flow and thereby have a change in flow that the ventilator 100 cannot detect. Accordingly, a monitored parameter below a minimum measurable value will not be detected by the ventilator 100.

According to an embodiment, a pressure-triggering method may involve the trigger module 115 of the ventilator 100 monitoring the circuit pressure, and detecting a slight drop in circuit pressure. The slight drop in circuit pressure may indicate that the patient's respiratory muscles are creating a slight negative pressure that in turn generates a pressure gradient between the patient's lungs and the airway opening in an effort to inspire. The ventilator 100 may interpret the slight drop in circuit pressure as a patient trigger and may consequently initiate inspiration by delivering respiratory gases.

Alternatively, the trigger module 115 of the ventilator 100 may detect a flow-triggered event. Specifically, the trigger module 115 of the ventilator 100 may monitor the circuit flow, as described above. If the ventilator 100 detects a slight drop in the base flow through the exhalation module during exhalation, this may indicate that the patient 150 is attempting to inspire. In this case, the ventilator 100 is detecting a drop in base flow attributable to a slight redirection of gases into the patient's lungs (in response to a slightly negative pressure gradient as discussed above). Accordingly, changes in base flow as instructed by the base flow trajectory module 118 may, if the trigger threshold is set too low, trigger an unwanted inspiration.

The inspiratory trigger trajectory module 117 (illustrated as the “ITT Module”) determines a patient initiated inspiration trigger threshold. The ITT module 117 sends the determined inspiration trigger threshold to another component of the ventilator, such as the controller 110, processor 116, and/or the trigger module 115. The trigger module 115, as discussed above, monitors the ventilator and/or patient parameters to determine if the parameters meet and/or exceed the inspiration trigger threshold. The ITT module 117 continuously updates the inspiration trigger threshold. Accordingly, the ITT module 117 may send different inspiration trigger thresholds during different portions of exhalation.

The ITT module 117 determines an initial inspiration trigger threshold while delivering the initial base flow. In some embodiments, the initial inspiration trigger threshold is input or selected by the operator. In other embodiments, the initial inspiration trigger threshold is determined by the ventilator 100 based on the configuration of the ventilator and/or based on ventilator parameters and/or patient parameters. The initial inspiration trigger is set during at least the first portion of exhalation, which includes at least the beginning or start of the exhalation period.

In some embodiments, in order to prevent undesirable early inspiration triggers, the inspiration trigger may be set relatively high. For example, in some embodiments, the initial inspiration trigger requires a change of flow of at least 6 liters per minute (LPM). In other embodiments, the initial inspiration trigger requires a change of flow of at least 8 LPM. In further embodiments, the initial inspiration trigger requires a change of flow of at least 10 LPM.

However, as the exhalation continues the likelihood that a patient desires to initiate an inspiration increases. Accordingly, the ITT module 117 decreases an inspiration trigger threshold during the second portion of exhalation. The decrease in the inspiration trigger threshold requires the patient to make less of an effort to trigger a desired inspiration during the second portion of exhalation. Thus, the ITT module 117 decreases an inspiration trigger threshold while the base flow trajectory module 118 increases the base flow delivered to the patient 150 as illustrated in FIG. 4.

In some embodiments, the ITT module 117 decreases the inspiration trigger at an exponential trajectory. In some embodiments, the exponential trajectory is based on a time constant. The time constant may be determined by the ventilator 100 based on the ventilator configuration or based on ventilator and/or patient parameters. In other embodiments, the time constant is input or selected by the operator. In some embodiments, the time constant utilized by the ITT module 117 is the same time constant utilized by the base flow trajectory module 118 to determine how to increase the amount of base flow delivered to the patient circuit tubing. In other embodiments, the ITT module 117 decreases an inspiration trigger threshold as a function of the amount the base flow trajectory module 118 increases base flow or instructs the inspiratory module 104 to increase base flow. In further embodiments, the ITT module 117 decreases an inspiration trigger threshold concurrently while the base flow trajectory module 118 increases the base flow delivered to the patient circuit tubing as illustrated in FIG. 4.

In some embodiments, the ITT module 117 also determines a first inspiration trigger threshold value, such as a desired inspiration trigger threshold. In some embodiments, the first inspiration trigger threshold value is input or selected by the operator. In other embodiments, the first inspiration trigger threshold value is determined by the ventilator 100 based on the configuration of the ventilator 100 and/or based on ventilator parameters and/or patient parameters. In embodiments with a first inspiration trigger threshold value, the ITT module 117 decreases the inspiration trigger threshold from the initial inspiration trigger threshold towards the first inspiration trigger threshold value, such as a desired inspiration trigger threshold.

Accordingly, in some embodiments, the ITT module 117 decreases the inspiration trigger threshold until the inspiration trigger essentially or substantially reaches the first inspiration trigger threshold value. Once the inspiration trigger threshold substantially reaches the first inspiration trigger threshold value, the ITT module 117 sets the inspiration trigger threshold value to the first inspiration trigger threshold value. The first inspiration trigger threshold value is substantially reached or essentially reached when the ventilator 100 can no longer decrease the inspiration trigger threshold without reaching or passing the first inspiration trigger threshold value based on the sensitivity and precision of the ventilator components.

ITT Module 117 decreases the inspiration trigger threshold while the base flow is being adjusted as a patient initiated inspiration trigger become more likely. The decrease in inspiration trigger threshold allows a patient to exert less effort to trigger a desired inspiration as a patient initiated inspiration trigger become more likely during the second portion of exhalation.

The base flow trajectory module 118 allows the ventilator 100 to reduce the amount of base flow delivered during exhalation. The smaller the ventilator-delivered base flow is during active exhalation, the smaller the uncertainty contributed by measuring base flow by different sensors 107 (once on the delivery side and a second time as a portion of exhaust gas on the exhalation side). This is particularly advantageous under neonatal conditions when tidal volumes and exhaled flow rates are relatively smaller and may be some orders of magnitude smaller than the base flow. Accordingly, the base flow trajectory module 118 allows the processor 116 or controller 110 to more accurately calculate exhaled tidal volume and/or spirometry than ventilators that utilize a constant base flow or a higher amount of base-flow during active exhalation.

FIG. 2 illustrates an embodiment of a method 200 for ventilating a patient with a ventilator. Method 200 begins at the start of exhalation. During exhalation the ventilator during method 200 delivers a set base flow to the patient during at least a first portion exhalation and delivers a base flow that varies over time during at least a second portion of exhalation. Further, during exhalation the ventilator during method 200 determines a set inspiration trigger threshold for at least a first portion exhalation and determines an inspiration trigger threshold that varies over time during at least a second portion of exhalation.

As illustrated, method 200 includes a first portion delivery operation 202. During the first portion delivery operation 202, the ventilator delivers an initial base flow to the patient circuit tubing during at least a first portion of exhalation. Further, the ventilator during the first portion delivery operation 202 determines an initial inspiratory trigger threshold for the first portion of exhalation.

The first portion of exhalation includes at least the beginning or start of exhalation and does not overlap with the second portion of exhalation. In some embodiments, the first portion of exhalation includes the minimum exhalation time. In some embodiments, the ventilator delivers the initial base flow to the patient at the start of or for the entire duration of a first portion of exhalation during first portion delivery operation 202.

The initial base flow and/or the initial inspiration trigger threshold may be predetermined by the ventilator based on the configuration of the ventilator or determined by the ventilator based on ventilator and/or patient parameters. In an alternative embodiment, the initial base flow and/or the initial inspiration trigger threshold may be input or selected by an operator.

In some embodiments, the initial base flow is a base flow of zero or close to zero. In other embodiments, the initial base flow is equal to an estimated leak flow. In some embodiments, the initial inspiration trigger threshold is set relatively high. During early exhalation it is unlikely that a patient actually intended to trigger an inspiration. Accordingly, to prevent monitored parameters from resulting in a false trigger of an undesired inspiration, a high initial inspiration trigger threshold may be utilized. For example, the initial inspiration trigger threshold may require a change of flow of at least 6 to 10 LPM.

Further, method 200 includes a transition condition decision operation 204 (illustrated as “transition condition?”). During the transition condition decision operation 204, the ventilator determines if a condition has been met. The first portion of exhalation ends when the condition has been met. The second portion of exhalation begins when the condition has been met.

In some embodiments, the condition includes determining that a minimum exhalation time has expired, determining that an exhalation flow is below the minimum exhalation flow, determining that the exhalation flow is below the minimum exhalation flow prior to expiration of a maximum exhalation time, and/or determining that the maximum exhalation time has expired. In other embodiments, the condition includes determining that a minimum exhalation time has expired and determining that either a monitored exhalation flow is below the minimum exhalation flow prior to expiration of a maximum exhalation time or the maximum exhalation time has expired.

If the ventilator during transition condition decision operation 204 determines that a condition has been met, the ventilator selects to perform second portion delivery operation 206. If the ventilator during transition condition decision operation 204 determines that a condition has not been met, the ventilator selects to perform inspiration trigger decision operation 208.

Method 200 includes an inspiration trigger decision operation 208 (illustrated as “Detect Insp. Trigger?”). During the inspiration trigger decision operation 208, the ventilator determines if an inspiration trigger has been detected. Inspiration trigger decision operation 208 is performed during the first portion of exhalation.

The order of the performance of the first portion delivery operation 202, transition condition decision operation 204, and the inspiration trigger decision operation 208 is irrelevant. Accordingly, the first portion delivery operation 202, transition condition decision operation 204, and the inspiration trigger decision operation 208 may be performed in any order, simultaneously, at different times, and/or at overlapping times. In some embodiments, the first portion delivery operation 202, transition condition decision operation 204, and the inspiration trigger decision operation 208 are each performed concurrently during the entire first portion of exhalation.

The ventilator during inspiration trigger decision operation 208 monitors patient and/or ventilator parameters to determine if an inspiratory trigger threshold has been met and/or exceeded during the first portion of exhalation. The inspiratory trigger threshold includes any suitable condition or threshold for determining that inspiration should be provided to the patient. During the first portion of exhalation, the inspiratory threshold includes the initial inspiratory trigger threshold as determined by first portion delivery operation 202.

In some embodiments, method 200 detects changes in a ventilator and/or patient parameter via the monitoring of a respiratory gas pressure, the monitoring of lung flow, direct or indirect measurement of nerve impulses, or any other suitable method for detecting changes in a ventilator parameter for comparison to inspiratory trigger thresholds. Method 200 may utilize sensors to monitor the ventilator and/or patient parameters. Sensors may include any suitable sensing device as known by a person of skill in the art for a ventilator. In some embodiments, the inspiration trigger threshold may be a change in exhalation pressure or a change in exhalation flow. In some embodiments, the sensors are located in the pneumatic system, the breathing circuit, and/or on the patient. In some embodiments, the ventilator monitors the exhalation flow and/or exhalation pressure every computational cycle (e.g., 2 milliseconds, 5 milliseconds, 10 milliseconds, etc.) during the delivery of exhalation to determine if the inspiration trigger threshold has been met and/or exceeded.

If the ventilator during inspiration trigger decision operation 208 determines that the ventilator and/or patient parameters do not meet or exceed an inspiration trigger threshold, the ventilator selects to perform first portion delivery operation 202. If the ventilator during inspiration trigger decision operation 208 determines that the ventilator and/or patient parameters do meet or exceed an inspiration threshold, the ventilator selects to perform inhale operation 210. The performance of the inhale operation 210 ends the exhalation of the patient.

As illustrated, method 200 includes a second portion delivery operation 206. During the second portion delivery operation 206, the ventilator increases the base flow delivered to the patient from the initial base flow toward a first flow value during the second portion of exhalation. In some embodiments, the ventilator increases base flow from the initial base flow toward the first flow value at the start of or during the entire duration of the second portion of exhalation during second portion delivery operation 206.

In some embodiments, the ventilator during second portion delivery operation 206 increases the base flow from the initial base flow towards the first flow value until the first flow value is reached or substantially reached. If the delivered base flow reaches or substantially reaches the first flow value, the ventilator during second portion delivery operation 206 delivers the first flow value.

In some embodiments, the ventilator during second portion delivery operation 206 increases the base flow at an exponential trajectory. In further embodiments, the ventilator during second portion delivery operation 206 increases the base flow at an exponential trajectory based on a time constant. The time constant may be predetermined by the ventilator based on the configuration of the ventilator or determined by the ventilator based on ventilator parameters and/or patient parameters. In an alternative embodiment, the time constant is input or selected by an operator.

Further, the ventilator during the second portion delivery operation 206 may determine a desired base flow and/or a desired trigger threshold. In embodiments, the desired base flow and/or the desired trigger threshold are received from input or a selection by an operator. The operator may input or select the desired base flow and/or the desired trigger threshold via a graphical user interface, keyboard, mouse, and/or any other suitable input device for receiving and interpreting operator commands, instructions, and/or selections. In an alternative embodiment, the desired base flow and/or desired inspiration trigger threshold are determined by the ventilator.

In some embodiments, the first flow value is the desired base flow. In these embodiments, the ventilator during second portion delivery operation 206 may increase the base flow from the initial base flow towards the desired base flow until the desired base flow is substantially reached.

Further, during the second portion delivery operation 206, the ventilator decreases an inspiration trigger threshold from the initial inspiration trigger threshold toward a first trigger threshold value during at least a portion of the second portion of exhalation. Accordingly, in some embodiments, the ventilator concurrently or simultaneously increases the delivered base flow as the ventilator lowers the inspiration trigger threshold during second portion delivery operation 206.

In some embodiments, the ventilator during second portion delivery operation 206 decreases the inspiration trigger threshold from the initial inspiration trigger threshold towards the first inspiration trigger threshold value until the first inspiration trigger threshold value is reached or substantially reached. If the set inspiration trigger threshold reaches or substantially reaches the first trigger threshold value, the ventilator during second portion delivery operation 206 sets the inspiration trigger threshold to the first trigger threshold value.

In some embodiments, the ventilator during second portion delivery operation 206 decreases the inspiration trigger threshold at an exponential trajectory. In further embodiments, the ventilator during second portion delivery operation 206 decreases the inspiration trigger threshold at an exponential trajectory based on a time constant. In some embodiments, the time constant is predetermined by the ventilator based on the configuration of the ventilator or determined by the ventilator based on ventilator and/or patient parameters. In further embodiments, the time constant may be the same time constant utilized by the ventilator to determine the amount to increase the delivered base flow. In additional embodiments, the ventilator during second portion delivery operation 206 decreases the inspiration trigger threshold based on a function of the amount the ventilator increased the delivered base flow.

In some embodiments, the first inspiration trigger threshold value is a desired inspiration trigger threshold. In these embodiments, the ventilator may decrease the inspiration trigger threshold from the initial inspiration trigger threshold towards the desired inspiration trigger threshold until the desired inspiration trigger threshold is substantially reached. If the set inspiration trigger threshold reaches or substantially reaches the desired inspiration trigger threshold, the ventilator during second portion delivery operation 206 sets the inspiration trigger threshold to the desired inspiration trigger threshold value.

As illustrated, method 200 includes an inspiration trigger decision operation 207 (illustrated as “Detect Insp. Trigger?”). During the inspiration trigger decision operation 207, which is similar to inspiration trigger decision operation 208, the ventilator determines if an inspiration trigger has been detected. Inspiration trigger decision operation 207 is performed during the second portion of exhalation.

The order of the performance of the second portion delivery operation 206 and the inspiration trigger decision operation 207 is irrelevant. Accordingly, the second portion delivery operation 206 and the inspiration trigger decision operation 207 may be performed in any order, simultaneously, at different times, and/or at overlapping times. In some embodiments, the second portion delivery operation 206 and the inspiration trigger decision operation 207 are each performed concurrently during the entire second portion of exhalation.

The ventilator during inspiration trigger decision operation 207 monitors patient and/or ventilator parameters to determine if an inspiratory trigger threshold has been met or exceeded during the second portion of exhalation. The inspiratory trigger threshold includes any suitable condition or threshold for determining that inspiration should be provided to the patient. During the second portion of exhalation, the inspiratory trigger threshold includes the varying inspiratory trigger threshold as determined by second portion delivery operation 206.

If the ventilator during inspiration trigger decision operation 208 determines that the ventilator and/or patient parameters do not meet or exceed the inspiration trigger threshold, the ventilator selects to perform second portion delivery operation 206. If the ventilator during inspiration trigger decision operation 207 determines that the ventilator and/or patient parameters do meet or exceed the inspiration threshold, the ventilator selects to perform inhale operation 210. The performance of the inhale operation 210 ends the exhalation of patient.

Method 200 includes inhale operation 210. The ventilator during inhale operation 210 provides inspiration to the patient and ends exhalation. The inspiration provided to the patient may be determined by the ventilator and/or operator input or selections. For example, the delivered inspiration may be based on a selected breath type or ventilation mode.

In some embodiments, method 200 includes an estimating operation and an adjusting operation. The ventilator during the estimating operation estimates the amount of flow leaked from a ventilation tubing system during ventilation. The ventilator may utilize any known methods for estimating the amount of flow leaked from the ventilation tubing system. The ventilator during the adjusting operation adds the estimated amount of leak flow to the initial base flow to account for the amount of flow leaked from the ventilation tubing system. Further, the ventilator during the adjusting operation may add the estimated amount of leak flow to a desired base flow or a first flow value to account for the amount of flow leaked from the ventilation tubing system.

In other embodiments, method 200 includes a display operation. The ventilator during the display operation displays any suitable information for display on a ventilator. In one embodiment, the display operation displays at least one of a minimum exhalation flow, a minimum exhalation time, a maximum exhalation time, a desired base flow, a desired inspiration trigger threshold, an inspiration trigger threshold, a base flow, an exhalation flow, an estimated leak flow, and an exhalation pressure.

Method 200 decreases the inspiration trigger threshold while the base flow is being adjusted since the longer the exhalation period, the more likely the patient will attempt to initiate an inspiration trigger. The decrease in the inspiration trigger threshold allows a patient to exert less effort to trigger a desired inspiration during the second portion of exhalation as it becomes more likely that a patient will attempt to trigger an inspiration.

Further, method 200 allows the ventilator to reduce the amount of base flow delivered during exhalation. The smaller the ventilator-delivered base flow is during active exhalation, the smaller the uncertainty contributed by measuring base flow by different sensors (once on the delivery side and a second time as a portion of exhaust gas on the exhalation side). This is particularly advantageous under neonatal conditions when tidal volumes and exhaled flow rates are relatively smaller and may be some orders of magnitude smaller than the base flow. Accordingly, method 200 allows the ventilator to more accurately calculate exhaled tidal volume and/or spirometry than ventilators that utilize a constant base flow or a higher amount of base-flow during active exhalation.

Accordingly, in some embodiments, method 200 includes a calculation operation. The ventilator during the calculation operation calculates an exhaled tidal volume. The ventilator may utilize any known methods for calculating exhaled tidal volume. In some embodiments, the ventilator during the calculation operation also calculates spirometry. In some embodiments, the spirometry calculation is based on the calculated exhaled tidal volume. The ventilator may utilize any known methods for calculating spirometry.

In some embodiments, a microprocessor-based ventilator that accesses a computer-readable medium having computer-executable instructions for performing the method of ventilating a patient with a medical ventilator is disclosed. This method includes repeatedly performing the steps disclosed in method 200 above and/or as illustrated in FIG. 2.

In some embodiments, the ventilator system includes: means for determining an initial base flow; means for determining an initial inspiration trigger threshold; means for delivering the initial base flow during at least a first portion of exhalation while setting the inspiration trigger threshold to the initial inspiration trigger threshold; means for increasing base flow from the initial base flow toward a first flow value during at least a second portion of exhalation; and means for decreasing the inspiration trigger threshold from the initial inspiration trigger threshold toward a first trigger threshold value while performing the step of increasing the base flow.

FIGS. 3A and 3B illustrate an embodiment of a method 300 for ventilating a patient with a ventilator. As illustrated, method 300 begins at the start of exhalation. As illustrated in FIG. 3A, method 300 includes an initial base flow deliver operation 302, determine initial inspiration trigger threshold operation 303, decision operation 304 (illustrated as “Detect Initial Insp. Trigger”), decision operation 306 (illustrated as “Min. Exh. Time Expired?”), decision operation 308 (illustrated as “Max. Exh. Time Expired?”), and decision operation 312 (illustrated as “Exh. Flow less than Max. Exh. Flow?”). During the initial base flow deliver operation 302, the ventilator delivers an initial base flow to the patient during exhalation during at least a first portion of exhalation. During the initial base flow deliver operation 302, the ventilator performs determine initial inspiration trigger threshold operation 303, decision operation 304, decision operation 306, decision operation 308, and decision operation 312.

The ventilator during the determine initial inspiration trigger threshold operation 303, determines an initial inspiration trigger threshold for the first portion of exhalation. In some embodiments, initial inspiration trigger threshold is determined by the ventilator. In other embodiments, initial inspiration trigger threshold is determined based on operator input or selection.

The ventilator during the decision operation 304 monitors patient and/or ventilator parameters to determine if an inspiratory trigger threshold has been met and/or exceeded during the first portion of exhalation. The inspiratory trigger threshold includes any suitable condition or threshold for determining that inspiration should be provided to the patient. During the first portion of exhalation, the inspiratory threshold includes the initial inspiratory trigger threshold as determined by determine initial inspiration trigger threshold operation 303. For example, the initial inspiration trigger threshold may require a change of flow of at least 6 to 10 LPM.

In some embodiments, method 300 detects changes in a ventilator and/or patient parameter during the decision operation 304 via the monitoring of a respiratory gas pressure, the monitoring of lung flow, direct or indirect measurement of nerve impulses, or any other suitable method for detecting changes in a ventilator parameter for comparison to inspiratory trigger thresholds. Method 300 may utilize sensors to monitor the ventilator and/or patient parameters. Sensors may include any suitable sensing device as known by a person of skill in the art for a ventilator. In some embodiments, the inspiration trigger threshold may be a change in exhalation pressure or a change in exhalation flow. In some embodiments, the sensors are located in the pneumatic system, the breathing circuit, and/or on the patient. In some embodiments, the ventilator monitors the exhalation flow and/or exhalation pressure every computational cycle (e.g., 2 milliseconds, 5 milliseconds, 10 milliseconds, etc.) during the delivery of exhalation to determine if the inspiration trigger threshold has been met and/or exceeded.

The ventilator during decision operation 304 compares the output of the one or more sensors to at least one inspiration trigger threshold. If the output meets and/or exceeds the one or more inspiration trigger threshold, the ventilator determines during decision operation 304 that an inspiration trigger is detected. If the output does not meet the one or more inspiration trigger thresholds, the ventilator determines during decision operation 304 that an inspiration trigger is not detected. If the ventilator determines that the inspiration trigger is detected during the decision operation 304, the ventilator selects to perform deliver inspiration operation 326 (illustrated as “Deliver Insp. Operation”). If the ventilator determines that the inspiration trigger is not detected during the decision operation 304, the ventilator selects to perform decision operation 306.

As illustrated in FIG. 3A, method 300 includes a deliver inspiration operation 326. The ventilator during deliver inspiration operation 326 delivers inspiration to the patient ending exhalation. The ventilator performs deliver inspiration operation 326 when a patient trigger is detected. The ventilator delivers an inspiration based on ventilator parameters, patient parameters, and/or input or selections from the operator. For example, the inspiration provided by the ventilator may be based on a selected breath type and/or mode of ventilation.

The ventilator during decision operation 306 determines if the minimum exhalation time has expired. As discussed above, the minimum exhalation time refers to a predetermined amount of time in which it is unlikely that a patient would desire to begin inspiration or would attempt to trigger an inspiration. If the ventilator determines that the minimum exhalation time has not expired during decision operation 306, the ventilator selects to perform decision operation 304. If the ventilator determines that the minimum exhalation time has expired during decision operation 306, the ventilator selects to perform decision operation 308. In some embodiments, the ventilator determines if the minimum exhalation time has expired by monitoring the output of sensors and/or by monitoring calculations based on the output of sensors.

The ventilator during decision operation 308 determines if the maximum exhalation time has expired. As discussed above, the maximum exhalation time refers to a predetermined amount of time after which it becomes highly likely that a patient would attempt to trigger inspiration. If the ventilator determines that the maximum exhalation time has not expired during decision operation 308, the ventilator selects to perform decision operation 312. If the ventilator determines that the maximum exhalation time has expired during decision operation 308, the ventilator selects to perform increasing base flow delivery operation 310 (illustrated as “Incr. Base Flow Deliver Operation). In some embodiments, the ventilator determines if the maximum exhalation time has expired by monitoring the output of sensors and/or by monitoring calculations based on the output of sensors.

The ventilator during decision operation 312 determines if the exhalation flow is below the minimum exhalation flow. In some embodiments, the ventilator determines the exhalation flow by monitoring the output of sensors and/or by monitoring calculations based on the output of sensors. The minimum exhalation flow refers to a predetermined flow rate that when exhaled by the patient indicates that a patient is approaching the end of active exhalation. In some embodiments, the minimum exhalation flow is zero. In some embodiments, the minimum exhalation flow is determined by the ventilator. In other embodiments, the minimum exhalation flow is set or determined by the operator via operator input or selection. If the ventilator determines that the exhalation flow is below the minimum exhalation flow during decision operation 312, the ventilator selects to perform increasing base flow delivery operation 310. If the ventilator determines that the exhalation flow is not below the minimum exhalation flow during decision operation 312, the ventilator selects to perform decision operation 304.

As further illustrated in FIG. 3A, method 300 includes an increasing base flow delivery operation 310 (illustrated as “Incr. Base Flow Deliver Operation). The ventilator during the increasing base flow delivery operation 310 increases the amount of base flow delivered to the patient during exhalation at an exponential trajectory from the initial base flow towards a desired base flow. The exponential trajectory is based on a time constant. The time constant is determined by the ventilator. In some embodiments, the desired base flow is determined by the ventilator. In other embodiments, the desired base flow is received by the ventilator via operator input or selection.

The increasing base flow delivery operation 310 is performed by the ventilator during at least a second portion of exhalation. During the increasing base flow delivery operation 310, the ventilator performs decreasing inspiration trigger threshold operation 314 (illustrated as “Deer. Insp. Trigger Operation”), decision operation 316 (illustrated as “Insp. Trigger Reach Desired Insp. Trigger?”), decision operation 318 (illustrated as “Base Flow reach Desired Base Flow?”), and decision operation 324 (illustrated as “Detect Insp. Trigger?”) as illustrated in FIG. 3B.

As illustrated in FIG. 3B, method 300 includes a decreasing inspiration trigger threshold operation 314. The ventilator during the decreasing inspiration trigger threshold operation 314 decreases the inspiration trigger threshold monitored by the ventilator during exhalation at an exponential trajectory from the initial inspiration trigger threshold towards a desired inspiration trigger threshold. The exponential trajectory is based on the same time constant as utilized by the ventilator during the increasing base flow delivery operation 310 to determine the base flow trajectory. In some embodiments, the desired inspiration trigger threshold is determined by the ventilator. In other embodiments, the desired inspiration trigger threshold is received by the ventilator via operator input or selection. As discussed above the ventilator performs decreasing inspiration trigger threshold operation 314 while performing the increasing base flow delivery operation 310. In some embodiments, the increasing base flow delivery operation 310 is performed concurrently with the decreasing inspiration trigger threshold operation 314 by the ventilator as illustrated in FIG. 4.

Method 300 includes a decision operation 316, decision operation 318, and decision operation 324. The order of the performance of the decision operation 316, the decision operation 318, and decision operation 324 is irrelevant. Accordingly, the decision operation 316, the decision operation 318, and decision operation 324 may be performed in any order, simultaneously, at different times, and/or at overlapping times. Further, the decision operation 316, the decision operation 318, and decision operation 324 are all performed during at least the second portion of exhalation.

The ventilator during decision operation 316 determines if the inspiration trigger threshold has substantially reached the desired inspiration threshold. The ventilator may determine if the inspiration trigger threshold has substantially reached a desired inspiration threshold. If the ventilator determines that the inspiration trigger threshold has substantially reached the desired inspiration threshold during decision operation 316, the ventilator selects to perform maintaining desired inspiration trigger threshold operation 322 (illustrated as “Maintain Desired Insp. Trigger Operation”). If the ventilator determines that the inspiration trigger threshold has not substantially reached the desired inspiration threshold during decision operation 316, the ventilator selects to perform decision operation 318.

Further, method 300 includes a maintaining desired inspiration trigger threshold operation 322. The ventilator during the maintaining desired inspiration trigger threshold operation 322 sets and holds the inspiration trigger threshold at the desired inspiration trigger threshold. The performance of the maintaining desired inspiration trigger threshold operation 322 ends the ventilator performance of the decreasing inspiration trigger threshold operation 314.

The ventilator during decision operation 318 determines if the delivered base flow has substantially reached the desired base flow. The ventilator may determine if the base flow has substantially reached the desired base flow by monitoring the output of one or more sensors or by monitoring calculations based on the output of one or more sensors. If the ventilator determines that the base flow has substantially reached the desired base flow during decision operation 318, the ventilator selects to perform desired base flow deliver operation 320. If the ventilator determines that the base flow has not substantially reached the desired base flow during decision operation 318, the ventilator selects to perform decision operation 324. As discussed above, the desired inspiration trigger threshold or the desired base flow is substantially reached when the ventilator can no longer increase the amount of base flow provided without reaching or exceeding the desired base flow or when ventilator can no longer decrease the inspiration trigger threshold without reaching or exceeding the desired inspiration trigger threshold based on the sensitivity and precision of the ventilator components.

As illustrated in FIG. 3B, method 300 includes a desired base flow deliver operation 320. The ventilator during the desired base flow deliver operation 320 sets and holds the base flow delivered to the patient during at the second portion of exhalation at the desired base flow. The performance of the desired base flow deliver operation 320 ends the ventilator performance of the increasing base flow delivery operation 310.

Method 300 includes a decision operation 324. The ventilator during the decision operation 324 monitors patient and/or ventilator parameters to determine if an inspiratory trigger threshold has been met and/or exceeded during the second portion of exhalation. The inspiratory trigger threshold includes any suitable condition or threshold for determining that inspiration should be provided to the patient. During the second portion of exhalation, the inspiratory threshold includes the varying inspiratory trigger threshold as determined by decreasing inspiration trigger threshold operation 314.

In some embodiments, method 300 detects changes in a ventilator and/or patient parameter during the decision operation 324 via the monitoring of a respiratory gas pressure, the monitoring of lung flow, direct or indirect measurement of nerve impulses, or any other suitable method for detecting changes in a ventilator parameter for comparison to inspiratory trigger thresholds. Method 300 may utilize sensors to monitor the ventilator and/or patient parameters. Sensors may include any suitable sensing device as known by a person of skill in the art for a ventilator. In some embodiments, the inspiration trigger threshold may be a change in exhalation pressure or a change in exhalation flow. In some embodiments, the sensors are located in the pneumatic system, the breathing circuit, and/or on the patient. In some embodiments, the ventilator monitors the exhalation flow and/or exhalation pressure every computational cycle (e.g., 2 milliseconds, 5 milliseconds, 10 milliseconds, etc.) during the delivery of exhalation to determine if the inspiration trigger threshold has been met and/or exceeded.

The ventilator during decision operation 324 compares the output of the one or more sensors to at least one inspiration trigger threshold. If the output meets and/or exceeds the one or more inspiration trigger threshold, the ventilator determines during decision operation 324 that an inspiration trigger is detected. If the output does not meet the one or more inspiration trigger thresholds, the ventilator determines during decision operation 324 that an inspiration trigger is not detected. If the ventilator determines that the inspiration trigger is detected during the decision operation 324, the ventilator selects to perform deliver inspiration operation 326 (illustrated as “Deliver Insp. Operation”). If the ventilator determines that the inspiration trigger is not detected during the decision operation 324, the ventilator selects to perform increasing base flow delivery operation 310 as illustrated in FIG. 3A.

In some embodiments, method 300 includes an estimating operation and an adjusting operation. The ventilator during the estimating operation estimates the amount of flow leaked from a ventilation tubing system during ventilation. The ventilator may utilize any known methods for estimating the amount of flow leaked from the ventilation tubing system. The ventilator during the adjusting operation adds the estimated amount of leak flow to the initial base flow to account for the amount of flow leaked from the ventilation tubing system. Further, the ventilator during the adjusting operation may add the estimated amount of leak flow to a desired base flow to account for the amount of flow leaked from the ventilation tubing system.

In other embodiments, method 300 includes a display operation. The ventilator during the display operation displays any suitable information for display on a ventilator. In one embodiment, the display operation displays at least one of a minimum exhalation flow, a minimum exhalation time, a maximum exhalation time, a desired base flow, a desired inspiration trigger threshold, an inspiration trigger threshold, a base flow, an exhalation flow, an estimated leak flow, and an exhalation pressure.

Method 300 decreases the inspiration trigger threshold while the base flow is being adjusted since the longer the exhalation period, the more likely the patient will attempt to initiate an inspiration trigger. The decrease in the inspiration trigger threshold allows a patient to exert less effort to trigger a desired inspiration during the second portion of exhalation as it becomes more likely that a patient will attempt to trigger an inspiration.

Further, method 300 allows the ventilator to reduce the amount of base, flow delivered during exhalation. The smaller the ventilator-delivered base flow is during active exhalation, the smaller the uncertainty contributed by measuring base flow by different sensors (once on the delivery side and a second time as a portion of exhaust gas on the exhalation side). This is particularly advantageous under neonatal conditions when tidal volumes and exhaled flow rates are relatively smaller and may be some orders of magnitude smaller than the base flow. Accordingly, method 300 allows the ventilator to more accurately calculate exhaled tidal volume and/or spirometry than ventilators that utilize a constant base flow or a higher amount of base-flow during active exhalation.

Accordingly, in some embodiments, method 300 includes a calculation operation. The ventilator during the calculation operation calculates an exhaled tidal volume. The ventilator may utilize any known methods for calculating exhaled tidal volume. In some embodiments, the ventilator during the calculation operation also calculates spirometry. In some embodiments, the spirometry calculation is based on the calculated exhaled tidal volume. The ventilator may utilize any known methods for calculating spirometry.

In other embodiments, a microprocessor-based ventilator that accesses a computer-readable medium having computer-executable instructions for performing the method of ventilating a patient with a ventilator is disclosed. This method includes repeatedly performing the steps disclosed in method 300 above and/or as illustrated in FIG. 3.

EXAMPLES Example 1

FIG. 4 illustrates an embodiment of a graph of delivered base flow and an inspiration trigger threshold over time during an exhalation. In this embodiment, the desired inspiration trigger threshold is 3 LPM and the desired base flow is 4.5 LPM. In this embodiment, the first portion of exhalation ends upon the occurrence of a condition, which starts the second portion of exhalation. According to the illustrated embodiment, the condition occurs at 350 milliseconds (ms). The condition may include determining that a minimum exhalation time has expired, determining that an exhalation flow is below the minimum exhalation flow, determining that the exhalation flow is below the minimum exhalation flow prior to expiration of a maximum exhalation time, and/or determining that the maximum exhalation time has expired.

In an embodiment as illustrated in FIG. 4, an initial inspiration trigger threshold of 10 LPM is set during the first portion of exhalation. As illustrated in FIG. 4, an initial base flow of 1.5 LPM is delivered during the first portion of exhalation. After the occurrence of the condition and during the second portion of exhalation, as illustrated in FIG. 4, the inspiration trigger threshold is decreased exponentially while the delivered base flow is increased exponentially to reach 4.5 LPM. The inspiration trigger threshold is decreased until the set inspiration trigger threshold reaches the desired inspiration trigger threshold (3 LPM). Once the inspiration trigger threshold reaches the desired inspiration trigger threshold, the inspiration trigger threshold is maintained at the desired inspiration trigger threshold. Further, the delivered base flow is increased until the delivered base flow reaches the desired base flow. Once the delivered base flow reaches the desired base flow, the delivered base flow is maintained at the desired base flow.

A patient initiated inspiration is not detected during the exhalation time shown in FIG. 4. If an inspiration trigger was detected, inspiration would be delivered upon detection ending the exhalation period.

Example 2

Example 2 illustrates an embodiment of a pseudo code for the systems and methods of the disclosure. The pseudo code illustrated below utilizes an algorithm that incorporates the following aspects:

-   -   1) Base flow is initiated after the flow rate being exhaled by         the patient has reduced to a minimum threshold, which indicates         that a patient is approaching the end of active exhalation;     -   2) Base flow will be delivered in accordance with an exponential         trajectory to reach a desired base flow within an optimum         interval to both maintain Positive End-Expiratory Pressure         (PEEP) and to minimize false triggering; and     -   3) An inspiration trigger threshold will be adaptively adjusted         (with an exponential trajectory) from a less sensitive threshold         (i.e., harder to trigger) at the start of exhalation phase and         decreasing smoothly to asymptote to a desired inspiration         trigger threshold by the end of active exhalation or after         allowing an optimum interval concomitant with reaching the final         base flow.         The pseudo code embodiment utilizing the algorithm described         above is listed below:

//initialize filteredSensEx (inspiration trigger threshold) = 10.0 LPM //calculate a new base flow reference: leakAdd = estimated Value (estimated leak from the ventilator tubing system); DesiredFlow = BaseFlow + leakAdd; MinQE (minimum exhalation flow) = 1.5 LPM; MinTE (minimum exhalation time) = 150 ms; Alpha (a constant) = 0.05; MaxTE (maximum exhalation time) = 500 ms; //every control cycle during exhalation phase execute the following. IF (neonatal) { IF (ExhTime < MinTE) { DesiredFlow = leakAdd; BaseFlowCheck = false; filteredBaseFlow = 0; Sensitivity = setSensitivity+filteredSensEx; } Else { IF (((Qexh < MinQE) AND (!BaseFlowCheck)) OR  (exhTime > MaxTE)) BaseFlowCheck = true; } IF (BaseFlowCheck) { filteredBaseFlow = filteredBaseFlow * (1−alpha) + alpha * baseFlow; DesiredFlow = filteredBaseFlow + leakAdd; Sensitivity = setSensitivity + filteredSenEx * (1−alpha); filteredSensEx = filtered SensEx * (1−alpha) } Else { DesiredFlow = leakAdd; } } // no change if Adult or Pediatric settings. The pseudo code provided above is not meant to be limiting. Further, while values are provided in the embodiment of the pseudo code above, these values are not meant to be limiting and may vary based on ventilator and/or patient parameters.

Those skilled in the art will recognize that the methods and systems of the present disclosure may be implemented in many manners and as such are not to be limited by the foregoing exemplary embodiments and examples. In other words, functional elements being performed by a single or multiple components, in various combinations of hardware and software or firmware, and individual functions, can be distributed among software applications at either the client or server level or both. In this regard, any number of the features of the different embodiments described herein may be combined into single or multiple embodiments, and alternate embodiments having fewer than or more than all of the features herein described are possible. Functionality may also be, in whole or in part, distributed among multiple components, in manners now known or to become known. Thus, myriad software/hardware/firmware combinations are possible in achieving the functions, features, interfaces and preferences described herein. Moreover, the scope of the present disclosure covers conventionally known manners for carrying out the described features and functions and interfaces, and those variations and modifications that may be made to the hardware or software firmware components described herein as would be understood by those skilled in the art now and hereafter.

Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the disclosure and as defined in the appended claims. While various embodiments have been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the present invention. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the disclosure and as defined in the claims. 

What is claimed is:
 1. A ventilator system for delivering breathing gases to a patient, the ventilator comprising at least one processor and at least one memory storing computer-executable instructions that, when executed by the at least one processor, cause the ventilator system to: deliver an initial base flow during at least a first portion of exhalation; set an inspiration trigger threshold to an initial inspiration trigger threshold; increase base flow from the initial base flow toward a desired base flow during at least a second portion of exhalation; decrease the inspiration trigger threshold from the initial inspiration trigger threshold toward a desired inspiration trigger threshold while increasing the base flow; and increase a sensitivity to a patient initiated trigger during at least the second portion of exhalation while increasing the base flow and decreasing the inspiration trigger threshold.
 2. The ventilator system of claim 1, wherein increasing the base flow includes increasing the base flow at a first exponential trajectory, and wherein decreasing the inspiration trigger threshold includes decreasing the inspiration trigger threshold at a second exponential trajectory.
 3. The ventilator system of claim 1, wherein the initial base flow is zero.
 4. The ventilator system of claim 1, wherein the second portion of exhalation begins upon occurrence of a condition, where the condition comprises at least one of: determining that a minimum exhalation time has expired; determining that exhalation flow is below a minimum exhalation flow; determining that exhalation flow is below the minimum exhalation flow prior to expiration of a maximum exhalation time; or determining that the maximum exhalation time has expired.
 5. The ventilator system of claim 1, the computer-executable instructions further causing the ventilator system to: estimate a leak flow from a ventilation tubing system; and adjust the initial base flow and the desired base flow to account for the estimated leak flow from the ventilation tubing system.
 6. A ventilator, comprising: a pressure generating system adapted to generate a flow of breathing gases; a ventilation tubing system including a patient interface for connecting the pressure generating system to a patient; a controller for controlling delivery of breathing gases to the patient, the controller operative to improve an accuracy of estimating an exhalation volume while ventilating a patient with the ventilator, the controller further operative to: deliver a first base flow during at least a first portion of exhalation; set an inspiration trigger threshold to a first inspiration trigger threshold; increase base flow from the first base flow toward a second base flow during at least a second portion of exhalation; decrease the inspiration trigger threshold from the first inspiration trigger threshold toward a second inspiration trigger threshold while increasing the base flow; and increase a sensitivity to a patient-initiated trigger during at least the second portion of exhalation while increasing the base flow and decreasing the inspiration trigger threshold.
 7. The ventilator of claim 6, wherein increasing the base flow includes increasing the base flow at a first exponential trajectory.
 8. The ventilator of claim 6, wherein increasing the base flow is performed until at least one of a desired base flow is substantially reached or an inspiration trigger is detected.
 9. The ventilator of claim 7, wherein decreasing the inspiration trigger threshold includes decreasing the inspiration trigger threshold at a second exponential trajectory.
 10. The ventilator of claim 6, wherein decreasing the inspiration trigger threshold is performed until at least one of a desired inspiration trigger threshold is substantially reached or an inspiration trigger is detected.
 11. The ventilator of claim 9, wherein a slope of the first exponential trajectory of the base flow and a slope of the second exponential trajectory of the inspiration trigger threshold are based on a time constant.
 12. The ventilator of claim 7, wherein a slope of the first exponential trajectory of the base flow is based on a constant.
 13. The ventilator of claim 6, wherein decreasing the inspiration trigger threshold includes decreasing the inspiration trigger threshold at an exponential trajectory until at least one of a desired inspiration trigger threshold is substantially reached or an inspiration trigger is detected.
 14. The ventilator of claim 6, wherein the first base flow is zero.
 15. The ventilator of claim 6, wherein the first inspiration trigger threshold is a change in flow of at least 6 LPM.
 16. The ventilator of claim 6, wherein the second portion of exhalation begins upon an occurrence of a condition, wherein the condition comprises at least one of: determining that a minimum exhalation time has expired; determining that a monitored exhalation flow is below a minimum exhalation flow; determining that the monitored exhalation flow is below the minimum exhalation flow prior to expiration of a maximum exhalation time; or determining that the maximum exhalation time has expired.
 17. The ventilator of claim 6, the controller further operative to: estimate a leak flow from the ventilation tubing system; and adjust the first base flow and the second base flow to account for the estimated leak flow from the ventilation tubing system.
 18. The ventilator of claim 6, wherein increasing the base flow and decreasing the inspiration trigger threshold are performed concurrently.
 19. The ventilator of claim 6, wherein the inspiration trigger threshold is at least one of a change in a monitored exhalation flow or a change in a monitored exhalation pressure.
 20. The ventilator of claim 6, the ventilator further operative to: calculate an estimated exhaled tidal volume of the patient. 